The present invention relates to an organic light emitting diode display.
The wide use of personal computers and televisions sets has been accompanied by a demand for lightweight and thin display devices. This demand has been met by flat panel displays such as liquid crystal displays (LCD), which often displaced the heavier and bulkier cathode ray tube displays (CRTs).
However, the LCD is a passive display device, so it may need an additional light source such as backlight. Also, the LCD has various problems such as a slow response time and a narrow viewing angle.
An organic light emitting diode (OLED) display is another type of a flat panel display which has recently showed much promise in addressing these problems. The OLED display includes an organic light emitting layer interposed between two electrodes. One of the two electrodes injects holes and the other electrode injects electrons into the light emitting layer. The injected electrons and holes recombine to form excitons and emit the released energy in the form of light.
Because the OLED display is self-emissive, an additional light source is not necessary, resulting in low power consumption. The OLED also has a high response speed, wide viewing angle, and high contrast ratio.
However, the lifetime of the OLED display is not optimal if the OLED combines different light emitting materials with different lifetimes for display of different colors, e.g. red, green and blue. In particular, the blue light emitting material may have a significantly shorter lifetime than the red and green light emitting materials.
To make the lifetimes more uniform, the pixels using materials with shorter lifetimes are made larger than the other pixels. This however may preclude patterning of the different light emitting organic materials with a single shadow mask. Also, the small size of the pixels with longer-lifetime materials reduces these pixels' lifetime and hence reduces the total lifetime of the OLED device.
The above information is only for explaining the background of the invention and is not necessarily prior art and is not necessarily known in this country to a person of ordinary skill in the art.
Some embodiments of the present invention provide OLED devices with longer lifetimes even when using conventional light emitting materials.
Some embodiments include an organic light emitting diode (OLED) display comprising a first pixel and a second pixel that are associated with respective different colors, each of the first and second pixels being for displaying its associated color, wherein each of the first and second pixels comprises: a first electrode; a second electrode facing the first electrode; and a light emitting member formed between the first electrode and the second electrode; wherein the light emitting member of the first pixel comprises: at least two light-emitting elements for emitting light of the color associated with the first pixel; and a charge generation layer between the at least two light-emitting elements; and wherein the light emitting-member of the second pixel has fewer light-emitting elements than the light-emitting member of the first pixel.
Some embodiments further comprise a third pixel associated with a color different from the first and second pixels' associated colors, the third pixel being for displaying its associated color; wherein the third pixel comprises: a first electrode; a second electrode facing the first electrode; and a light emitting member formed between the first electrode and the second electrode; wherein the light emitting-member of the third pixel has fewer light-emitting elements than the light-emitting member of the first pixel.
In some embodiments, the first electrodes of the first, second and third pixels are parts of a common electrode.
In some embodiments, each light-emitting element of the first pixel has a shorter lifetime than each light-emitting element of the second and third pixels.
In some embodiments, the light-emitting elements of the first pixel, the second pixel, and the third pixel are for respectively emitting blue, red, and green light.
In some embodiments, the at least two light emitting elements of the first pixel comprise a first light-emitting element between the first pixel's first electrode and the charge generation layer and also comprise and a second light-emitting element between the charge generation layer and the first pixel's second electrode; the light emitting member of the first pixel further comprises an auxiliary layer formed between the first pixel's first electrode and the first light-emitting element or between the first light-emitting element and the charge generation layer or between the charge generation layer and the second light-emitting element or between the second light-emitting element and the first pixel's second electrode; the light emitting member of the second pixel further comprises an auxiliary layer formed between the second pixel's first electrode and the second pixel's one or more light-emitting elements or between the second pixel's one or more light-emitting elements and the second pixel's second electrode; and the light emitting member of the third pixel comprises an auxiliary layer formed between the third pixel's first electrode and the third pixel's one or more light-emitting elements or between the third pixel's one or more light-emitting elements and the third pixel's second electrode.
In some embodiments, the light emitting member of the first pixel is thicker than the light emitting members of the second and third pixels.
In some embodiments, the light emitting members of the second pixel and the third pixel have substantially the same thickness.
In some embodiments, the first, second, and third pixels have substantially equal areas.
In some embodiments, the first, second, and third pixels each include a driving transistor connected to the respective pixel's first electrode, and the OLED display further comprises circuitry for providing a first driving voltage to the driving transistor of the first pixel and for providing a second driving voltage different from the first driving voltage to the driving transistors of the second and third pixels.
In some embodiments, the circuitry comprises: a first driving voltage line connected to the driving transistor of the first pixel for transmitting the first driving voltage; and a second driving voltage line connected to the driving transistors of the second and third pixels for transmitting the second driving voltage.
In some embodiments, the first, second, and third pixels each include a driving transistor connected to the respective pixel's first electrode, and the OLED display further comprises circuitry for generating data signals in response to luminance levels and supplying the data signals to the driving transistors, wherein for any luminance level, the corresponding data signal for the driving transistor of the first pixel has a larger voltage than the corresponding data signal for the driving transistor of each of the second and third pixels.
Some embodiments include an OLED display comprising: a first pixel and a second pixel, wherein each of the first and second pixels comprises: a driving transistor; and one or more light-emitting elements connected to the driving transistor; wherein the first pixel comprises at least two light-emitting elements for emitting a color associated with the first pixel, and also comprises a charge generation layer disposed between the at least two light-emitting elements; and each light-emitting element of the first pixel has a shorter lifetime than each light-emitting element of the second pixel.
Some embodiments further comprise a third pixel comprising a driving transistor and one or more light-emitting elements connected to the driving transistor; wherein each light-emitting element of the first pixel has a shorter lifetime than each light-emitting element of the third pixel.
In some embodiments, the light-emitting elements of the first pixel, the second pixel, and the third pixel are for respectively emitting blue, red, and green light.
In some embodiments, wherein the first, second, and third pixels have substantially equal areas.
In some embodiments, a combined thickness of the one or more light emitting elements in the first pixel is greater than in the second pixel and greater than in the third pixel.
Some embodiments further comprise circuitry for providing a first driving voltage to the driving transistor of the first pixel and for providing a second driving voltage different from the first driving voltage to the driving transistors of the second and third pixels.
In some embodiments, the circuitry comprises: a first driving voltage line connected to the driving transistor of the first pixel for transmitting the first driving voltage; and a second driving voltage line connected to the driving transistors of the second and third pixels for transmitting the second driving voltage.
Some embodiments further comprise circuitry for generating data signals in response to luminance levels and supplying the data signals to the driving transistors, wherein for any luminance level, the corresponding data signal for the driving transistor of the first pixel has a larger voltage than the corresponding data signal for the driving transistor of each of the second and third pixels.
Some embodiments include an OLED display comprising: (1) a first pixel comprising: a driving transistor; and at least two light-emitting diodes connected to the driving transistor; (2) a second pixel comprising: a driving transistor; and only one light-emitting diode, said only one light-emitting diode being connected to the second pixel's driving transistor; wherein each light-emitting diode of the first pixel has a shorter lifetime than the light-emitting diode of the second pixel, and (3) circuitry for supplying a first driving voltage to the driving transistor of the first pixel and for supplying a second driving voltage different from the first driving voltage to the driving transistor of the second pixel.
Some embodiments further comprise: a third pixel comprising: a driving transistor; and only one light-emitting diode; wherein the the third pixel's light-emitting diode is connected to the third pixel's driving transistor; wherein each light-emitting diode of the first pixel has a shorter lifetime than the light-emitting diode of the third pixel, and said circuitry is for supplying the second driving voltage to the driving transistor of the third pixel.
In some embodiments, said circuitry comprises: a first driving voltage line connected to the driving transistor of the first pixel for transmitting the first driving voltage, and a second driving voltage line connected to the driving transistors of the second and the third pixel for transmitting the second driving voltage.
In some embodiments, the first pixel comprises: first and second light-emitting elements for emitting light of the same color; a first electrode disposed under the first light-emitting element; a second electrode disposed over the second light-emitting element; and a charge generation layer disposed between the first and second light-emitting elements, wherein the first electrode, the first light-emitting element, and the charge generation layer form one of the two light emitting diodes of the first pixel, and the charge generation layer, the second light-emitting element, and the second electrode form the other one of the two light emitting diodes of the first pixel.
Some embodiments include an OLED display comprising: a first pixel and a second pixel, wherein each of the first and second pixels comprises: a driving transistor; and one or more light-emitting elements connected to the driving transistor; wherein at least on light-emitting element of the first pixel has a shorter lifetime than at least one light-emitting element of the second pixel, and wherein the OLED display further comprises circuitry for generating data signals in response to luminance levels and supplying the data signals to the driving transistors, wherein for a given luminance level, the corresponding data signal for the driving transistor of the first pixel has a larger voltage than the corresponding data signal for the driving transistor of the second pixel.
Some embodiments further comprise a third pixel which comprises a driving transistor and one or more light-emitting elements connected to the driving transistor, wherein the circuitry is for generating and supplying the data signals to the driving transistor of the third pixel, wherein for a given luminance level, the corresponding data signal for the driving transistor of the first pixel has a larger voltage than the corresponding data signal for the driving transistor of the third pixel.
In some embodiments, the one or more light-emitting elements of the first pixel comprise first and second light-emitting elements for emitting light of the same color; wherein the first pixel further comprises: a first electrode disposed under the first light-emitting element; a second electrode disposed on the second light-emitting element; and a charge generation layer disposed between the first and second light-emitting elements, wherein the first electrode, the first light-emitting element, and the charge generation layer form a first light emitting diode, and the charge generation layer, the second light-emitting element, and the second electrode form a second light emitting diode.
Some embodiments include a method for operating an OLED display, the method comprising providing the first driving voltage to the driving transistor of the first pixel and providing the second driving voltage to the driving transistors of the second and third pixels.
Some embodiments include a method for operating the OLED display, the method comprising providing different data signals to the first pixel and at least one of the second and third pixels for a given luminance level.
In some embodiments, the lifetime of the display device may be increased, and the areas of all pixels may be optimally designed to reduce the cost and time required to manufacture the display.
The invention is not limited to embodiments having the advantages described above. Other features are described below. The invention is defined by the appended claims.